Merge pull request #272585 from hariramt/task/OnlineUpdate-18thApril

Online doc update

Author: prmerger-automator[bot]

articles/postgresql/migrate/migration-service/best-practices-migration-service-postgresql.md

@@ -164,9 +164,11 @@ Regularly incorporating these vacuuming strategies ensures a well-maintained Pos
 
 There are special conditions that typically refer to unique circumstances, configurations, or prerequisites that learners need to be aware of before proceeding with a tutorial or module. These conditions could include specific software versions, hardware requirements, or additional tools that are necessary for successful completion of the learning content.
 
-### Use of Replica Identity for Online migration
+### Online migration
 
-Online migration makes use of logical replication, which has a few [restrictions](https://www.postgresql.org/docs/current/logical-replication-restrictions.html). In addition, it's recommended to have a primary key in all the tables of a database undergoing Online migration. If primary key is absent, the deficiency may result in only insert operations being reflected during migration, excluding updates or deletes. Add a temporary primary key to the relevant tables before proceeding with the online migration. Another option is to use the [REPLICA IDENTIY](https://www.postgresql.org/docs/current/sql-altertable.html#SQL-ALTERTABLE-REPLICA-IDENTITY) action with `ALTER TABLE`. If none of these options work, perform an offline migration as an alternative.
+Online migration makes use of [pgcopydb follow](https://pgcopydb.readthedocs.io/en/latest/ref/pgcopydb_follow.html) and some of the [logical decoding restrictions](https://pgcopydb.readthedocs.io/en/latest/ref/pgcopydb_follow.html#pgcopydb-follow) apply. In addition, it's recommended to have a primary key in all the tables of a database undergoing Online migration. If primary key is absent, the deficiency may result in only insert operations being reflected during migration, excluding updates or deletes. Add a temporary primary key to the relevant tables before proceeding with the online migration.
+
+An alternative is to use the `ALTER TABLE` command where the action is [REPLICA IDENTIY](https://www.postgresql.org/docs/current/sql-altertable.html#SQL-ALTERTABLE-REPLICA-IDENTITY) with the `FULL` option. The `FULL` option records the old values of all columns in the row so that even in the absence of a Primary key, all CRUD operations are reflected on the target during the Online migration. If none of these options work, perform an offline migration as an alternative.
 
 ### Database with postgres_fdw extension
 

articles/postgresql/migrate/migration-service/concepts-known-issues-migration-service.md

@@ -27,9 +27,9 @@ Here are common limitations that apply to migration scenarios:
 
 - The migration service only migrates user databases, not system databases such as template_0 and template_1.
 
-- The migration service doesn't support moving POSTGIS, TIMESCALEDB, POSTGIS_TOPOLOGY, POSTGIS_TIGER_GEOCODER, PG_PARTMAN extensions from source to target.
+- The migration service doesn't support moving TIMESCALEDB, POSTGIS_TOPOLOGY, POSTGIS_TIGER_GEOCODER, PG_PARTMAN extensions from source to target.
 
-- You can't move extensions not supported by the Azure Database for PostgreSQL – Flexible server. The supported extensions are in [Extensions - Azure Database for PostgreSQL](/azure/postgresql/flexible-server/concepts-extensions).
+- You can't move extensions not supported by the Azure Database for PostgreSQL – Flexible server. The supported extensions are listed in [Extensions - Azure Database for PostgreSQL](/azure/postgresql/flexible-server/concepts-extensions).
 
 - User-defined collations can't be migrated into Azure Database for PostgreSQL – flexible server.
 
@@ -51,7 +51,7 @@ Here are common limitations that apply to migration scenarios:
 
 - The migration service is unable to perform migration when the source database is Azure Database for PostgreSQL single server with no public access or is an on-premises/AWS using a private IP, and the target Azure Database for PostgreSQL Flexible Server is accessible only through a private endpoint.
 
-- Migration to burstable SKUs isn't supported; databases must first be migrated to a nonburstable SKU and then scaled down if needed.
+- Migration to burstable SKUs isn't supported; databases must first be migrated to a non-burstable SKU and then scaled down if needed.
 
 ## Limitations migrating from Azure Database for PostgreSQL single server
 
@@ -61,6 +61,8 @@ Here are common limitations that apply to migration scenarios:
 
 - If the target flexible server uses SCRAM-SHA-256 password encryption method, connection to flexible server using the users/roles on single server fails since the passwords are encrypted using md5 algorithm. To mitigate this limitation, choose the option MD5 for password_encryption server parameter on your flexible server.
 
+- Online migration makes use of [pgcopydb follow](https://pgcopydb.readthedocs.io/en/latest/ref/pgcopydb_follow.html) and some of the [logical decoding restrictions](https://pgcopydb.readthedocs.io/en/latest/ref/pgcopydb_follow.html#pgcopydb-follow) apply.
+
 ## Related content
 
 - [Migration service](concepts-migration-service-postgresql.md)